Gas module orifice automated test fixture

ABSTRACT

A test fixture for a laser gas module offers automatic and manual testing for individual gas module components. Check or pressure relief valves are tested with an increasing pressure ramp caused by a metered gas flow into a ballast tank. Metering orifices are tested by measuring pressure change in a known volume tank as gas to or from the tank is directed through the orifice under test. The fixture includes capability to test valve logic and leakages. Test sequence and results are monitored on a computer display showing a schematic representation of both module and fixture. Manual control of module and fixture components is done via a computer graphic interface.

RELATED APPLICATION

This application is a divisional application of U.S. patent applicationSer. No. 09/306,053, filed May 6, 1999, entitled “Gas Module ValveAutomated Test Fixture.”

FIELD OF INVENTION

The invention relates to test equipment for a gas module, and morespecifically the invention relates to test equipment for gas supplysystems in gas discharge lasers.

BACKGROUND

Gas discharge lasers, such as excimer lasers, are used in industrialapplications. These applications include use in stepper systems forultra large scale integrated circuit manufacturing. In such industrialapplications it is extremely important to precisely control laser beampulse energy and wavelength in order to ensure consistent processingquality for each wafer. Laser beam quality is critically dependent onaccurate and precise control of gas mixture and pressure in the laserdischarge chamber.

FIG. 1 shows an excimer laser system used as a stepper systemillumination source. Gas control unit (or gas module) 101 in lasersystem 102 is subject to testing by the present invention. Laser system102 produces laser output beam L used by stepper 103. Stepper controlunit 104 uses a signal to trigger laser control unit 105 to generate alaser pulse. Laser control unit 105 then signals power source 106 toprovide a controlled voltage pulse to lasing unit 107. Lasing unit 107comprises a laser chamber, optical resonator, and other conventionallaser beam generation components. Lasing unit 107 sends signals to lasercontrol unit 105 that indicate the status of lasing unit 107 componentsand gas mixtures.

The laser chamber in lasing unit 107 is filled with a laser gas having aprecise pressure and mixture. Gas mixtures are typicallykrypton-fluorine or other conventional rare gas/halide laser gasmixtures. Control circuits excite the laser gas mixture by applying avoltage discharge pulse of predetermined width and interval acrosselectrodes (not shown). The voltage discharge pulse excites anoscillation in the resonating chamber and thereby creates a laser beam.

Gas control unit 101 helps to ensure constant laser beam energy andbandwidth by replacing laser chamber gases consumed during laser beamgeneration. Gas control unit 101 receives control signals from controlunit 105 to supply the proper gas mixture and pressure to lasing unit107. Laser control unit 105 receives signals from gas control unit 101indicating operating status and gas pressures in gas control unit 101.Gas control unit 101 must limit mass flow rates and control the mixtureratio of gases supplied to the laser chamber. In addition, gas controlunit 101 must provide a capability for handling dangerous gases, such asfluorine, typically used in gas discharge lasers. And, gas control unit101 must provide for gas evacuation from the laser beam generationequipment in lasing unit 107 under both normal and emergency conditions.

To Applicants' knowledge, no procedures or equipment were developed tocharacterize and test the critical gas control unit 101 prior to thepresent invention. In addition, no single piece of test equipmentexisted that was capable of performing a comprehensive test of a gasmodule such as gas control unit 101.

The challenge, therefore, was to create a test fixture and evaluationmethods capable of ensuring proper gas control unit function duringproduction operations using the laser beam. A further challenge was tocreate a test fixture and evaluation methods that allow gas module testsand measurement for use during engineering development.

SUMMARY

One embodiment of the present invention provides apparatus and methodsfor testing a gas discharge laser gas control module. Testing may beaccomplished in accordance with the present invention by using a singletest fixture. A test operator may test a gas module using automatic ormanual functions, or a combination of both. Functional tests includeevaluating gas control module leakage, valve logic, electrical wiringand connections, valve operation, pump operation, and metering orificediameters. Test data are acquired, stored, manipulated, and displayed toproduce information useful during both production and engineeringdevelopment.

Gas module leakage may be tested by pressurizing gas module componentsusing nitrogen gas and monitoring for pressure drops. Additional leaktests may be accomplished in embodiments having a built-in heliumdetector for use in conventional helium leak testing.

Valve logic and electrical circuit tests ensure a given control signalactivates the proper valve. A pressurized gas may be applied to a closedvalve. When a control signal is applied to open the valve, eitherdirectly as in a solenoid valve or indirectly as in a pneumaticallyactuated valve, gas pressure is monitored to check proper valvefunction.

Check valves and pressure relief valves may be tested both for leakage(reverse flow pressure test) and for correct opening pressure (forwardflow pressure test). Opening pressure may be checked by applying anincreasing pressure ramp to the valve under test and monitoring thepressure difference between upstream and downstream pressure readings ofgas flow through the valve. The increasing pressure ramp may be suppliedusing a controlled gas fill rate into a ballast tank.

Orifice diameter testing may be done by monitoring either the gas fillor discharge rate of a gas container through the orifice under test. Gaspressures above and below the orifice under test may be monitored andcompared to known calibration readings. From this pressure information acomputing system may calculate an accurate average diameter of theorifice under test.

Information such as analog output signals from pressure transducers maybe sampled and stored in a test fixture memory storage area. Thisinformation may be used to calculate test results that are subsequentlydisplayed in graphic format.

Test fixture control may be accomplished through a computer graphicaluser interface. In some embodiments, a schematic of the gas controlmodule and the test fixture is displayed. These embodiments may includecapability for operating both gas module and test fixture componentsusing the graphic interface. An operator may monitor automatic testsequences by viewing the display as well. Test fixture operation may beaccomplished using a computer control system that controls thegas-related plumbing and monitors data collection devices withelectronic interfaces.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an excimer laser system used as astepper system illumination source, with the laser system having a gascontrol unit subject to test using the present invention.

FIG. 2 is a schematic representation of a gas module.

FIG. 3A is a component diagram showing an embodiment of the presentinvention used for check valve and pressure relief valve testing.

FIG. 3B is a representation of a check valve differential pressuredisplay.

FIG. 4 is a diagram showing an embodiment of the present invention usedfor orifice diameter testing.

FIGS. 5A and 5B combined are a schematic showing an embodiment of thepresent invention.

FIG. 6 is a block diagram showing an embodiment of the presentinvention.

DETAILED DESCRIPTION

In order to describe test fixtures and methods in accordance with thepresent invention, we first explain a specific representative gasmodule. Following this explanation, we continue the detailed descriptionand explain how we test specific representative gas module components.Those skilled in the art will understand, however, that many embodimentsmay exist within the present invention's spirit and scope as describedfor specific embodiments below. Embodiments of this invention are notlimited to testing the specific gas module shown here.

The terms sensor and transducer are used interchangeably throughout thedetailed description. Furthermore, references to actions by a testoperator may refer either to manual or automatically controlledoperation.

I. Gas Module Description

FIG. 2 is a schematic representation of a typical gas module 200. Themodule contains laser gas panel 201, pump/halogen scrubber panel 203,and nitrogen panel 205. The solid lines represent pipes or tubes capableof carrying a gas flow. In addition, FIG. 2 uses the followingfunctional symbols for gas module 200 components:

BH: Bulkhead Gas Fitting

CV: Check Valve

F: Filter

G: Pressure Gauge

HS: Halogen Scrubber

MV: The Output Coupling on a Conventional Rotameter.

OR: Orifice or Adjustable Needle Valve

P: Pump

PAV: Pneumatic Actuated Valve. In this representation, a PAV is actuatedby pressurized dried nitrogen supplied through a solenoid valve.

PS: Pressure Sensor. These are gas pressure transducers that produce ananalog output electrical signal. The PS analog output signals aretypically used by laser control module 102 (FIG. 1), and during testingprocedures for data acquisition.

R: Manual pressure regulator

RO: Rotameter. Name for a mechanical device used to set and measure gasflow. A rotameter is a gauge in which a ball is suspended by a gasflowing upward in a conical bore so that the ball's height indicates gasflow volume.

SG: A gauge not used in relation to this invention.

SO: Shut Off valve

SV: Solenoid valve. Electrically actuated valve controlling gas flow toa Pneumatic Actuated Valve or other component.

V: Vent fitting.

In addition, FIG. 2 shows part of the laser system itself, representedby “Reinforced Metal Bellows Flexible Line”, SO2, BH9, SO3, G1, PS4,Laser Chamber 208, “Cooling System”, and laser shutter 212. Thesecomponents are not gas module 200 components, but are included to showgas module 200's relation to the laser system components that use thesupplied gas mixture.

Within gas module 200, nitrogen panel 205 provides controlled, pressureregulated nitrogen gas for various uses. Gas module 200 uses nitrogengas to control laser gas panel 201 pneumatic activated valves (PAVs).The laser generating system 101 (FIG. 1) uses nitrogen for cooling andto activate laser shutter 212. In addition, a user may require nitrogengas for other applications.

Nitrogen gas enters nitrogen panel 205 through fitting BH7 and filterF3. Check valve CV6 provides overpressure protection, allowing highpressure gas to vent through fitting V1. Valve SV8 controls nitrogen gasflow to manifold 214. Regulator R1 is manually activated and gauge G2indicates regulator R1 gas pressure setting. Sensor PS3 measuresnitrogen gas pressure in manifold 214.

Nitrogen panel 205 allows pressure regulated nitrogen gas to be directedin several ways after reaching manifold 214. First, nitrogen gas isavailable to solenoid valves SV1-SVG6 for use in activating pneumaticactuated valves PAV1-PAV6, respectively, in laser gas panel 201. When anopening signal is applied to a solenoid valve, nitrogen gas flows frommanifold 214 through the open solenoid valve and is carried via a pipeor tube (not shown) to the corresponding PAV. When the PAV receivessufficient gas pressure, it opens. Second, nitrogen gas from manifold214 is available to control gas-activated laser shutter 212. Nitrogengas is directed to shutter 212 through solenoid valve SV7, orifice OR6,and fitting BH10. Opening and closing signals to valve SV7 controlnitrogen gas flow for shutter 212 activation. Manually operated orificeOR6 protects shutter 212's operating mechanism (not shown) by limitinggas flow. Valve CV7 is not essential to operation. It is a component ofthe standard LEGRIS fitting selected for bulkhead mounting. The LEGRISfitting, known to those skilled in the art, provides a push-inconnection for a plastic tube, as well as the needle valve, in a compactand economical package. CV7 is tested to verify it does not defeat thefitting's needle valve metering operation. Third, nitrogen gas frommanifold 214 is available to a laser cooling system (not shown) throughfitting BH8. Finally, nitrogen gas from manifold 214 is available forother discretionary uses via filter F2, rotameters RO1-RO4, and fittingsMV1-MV4.

Laser gas panel 201 receives premixed gases, combines them into a singlegas mixture having a precise ratio and pressure, and provides them tothe laser system chamber 208. The gas mixtures and pressure is typicallycontrolled by a laser control unit (102, FIG. 1). As depicted, threepremixed gases enter laser gas panel 201 through fittings BH1, BH2, andBH3. Neon/fluorine gas enters through BH1, neon/krypton gas through BH2,and helium gas through BH3. BH1-3 are standard ¼-inch faceseal fittings,such as VCR fittings supplied by the Cajon Co. These are screw-onfittings using a nickel gasket as a seal. Nickel is chosen in order toeliminate any organic materials and because it is more corrosionresistant to strong oxidizing gases such as fluorine.

The three gases flow through fittings BH1, BH2, and BH3 to orifices OR1,OR2, and OR3, respectively. The orifices OR1, OR2, and OR3 are 0.063inch diameter round orifices. Their function is to limit the premixedgas input mass flows. Next, the three gasses flow through check valvesCV1, CV2, and CV3 to valves PAV1, PAV2, and PAV3, respectively. ValvesCV1, CV2, and CV3 are typically high flow, ball-type, one-third (⅓)pound per square inch (psi) pressure-actuated one-way valves. Theirpurpose is to prevent gas mixture back-flush out of manifold 202.

Electrically actuated solenoid valves SV1-6 drivepneumatically-activated valves PAV1-6 using nitrogen as discussed above(connection not shown). PAV1-PAV3 control individual premixed gas flowinto manifold 202. After the gasses pass through valves PAV1, PAV2, andPAV3 they become mixed in manifold 202. An external controller (notshown) optoelectrically monitors gas concentration levels in laserchamber 208, and subsequently activates valves PAV1, PAV2, and PAV3 toproduce a desired laser chamber 208 gas mixture ratio. Sensor PS1measures manifold 202 gas mixture pressure and produces a signalindicating sensed pressure. Sensor PS1 and sensor PS2 described beloware selected to withstand gas pressures significantly below oneatmosphere, although readings at such low pressures may be inaccurate.

As shown, laser gas panel 201 provides a laser gas mixture to a lasersystem running on neon/fluorine and neon/krypton gas mixtures. Fluorineis consumed during laser operation, so a laser control unit must makesmall incremental adjustments to the fluorine/krypton gas mixture toensure a constant mixture ratio. From manifold 202, the gas mixture isrouted to line 204 and then to chamber 208 through valves PAV5 and PAV6.Valve PAV5 provides a way to fill laser chamber 208 quickly, for exampleon initial start-up. PAV6 provides a way to let in small fluorine andkrypton gas mixture adjustment levels. Orifice OR4 controls this smalladjustment flow, and has a 0.013-inch diameter. A regulating orifice isused because the pneumatically-actuated valves are on-off, notproportional valves. Thus a laser control unit (102, FIG. 1) obtains abetter gas mixture resolution by using a flow restricting orifice. Thelaser control unit typically directs the gas module to use small,incremental gas mixture puffs, supplied by quickly opening and closing apneumatic valve, to control gas mixture and pressure in a laser chamber.

In order for the laser system control unit (102, FIG. 1) to ensure laserchamber 208 receives a proper gas mixture, accurate gas module 200orifice diameters are critical. When the orifice diameters are offspecification, laser control unit 102 (FIG. 1) has great difficultydetermining what gas mixture adjustments to make. Thus orifices OR1,OR2, OR3, and especially OR4 (the fine control) must meet stricttolerances.

Investigation revealed that both laser perforated and mechanicallydrilled orifice diameters vary a great deal. In addition, investigationfound that an orifice may become cone shaped if the nickel plate inwhich the orifice is drilled is overcompressed. That is, overtighteningmay dramatically change the orifice cross section. This cross sectiondeformation is caused by the way a conventional faceseal fitting ismade. Although this deformation is an important limitation for 0.063inch orifices, it is especially critical for 0.013 inch orifices.Investigation found a 50-60 percent variation in actual averagediameters for the 0.013 inch orifices.

Valve PAV4, either alone or in combination with valve PAV5, provides away to bleed pressure off the system through pump/halogen panel 203.Check valve CV4 is rated at approximately 20 psi (or 1-2 atmospheres)and provides overpressure protection for manifold 202 and lasercomponents (not shown) in chamber 208.

Valve SO1 is an emergency manual dump valve that is a safety feature. Inthe event the laser loses power, valve SO1 provides a way to quicklybleed off fluorine from laser chamber 208 through pump/halogen scrubberpanel 203. Using valve SO1 guarantees that no fluorine remains in thesystem in case of a leak or if a technician subsequently opens theplumbing at any point. Even small amounts of fluorine combined with anywater will create highly corrosive hydrofluoric acid. If an operatoropens valve SO1, pressure dumps through orifice OR5. Orifice OR5 has a0.063 inch diameter to prevent large impulse flows, thereby protectingthe optics in chamber 208 (not shown) and the halogen scrubber HS1.

Pump/halogen scrubber panel 203 includes a pump P1 and a scrubber HS1.Pump P1 is a vacuum pump. Scrubber HS1 is a fluorine removal canister.When laser chamber 208 is cleaned, pump P1 pumps chamber 208 to a lowpressure in the range of hundreds of millitorr. Scrubber HS1 provides away to ensure that all system portions may safely vent fluorine. Notethat shunt 210 is not in place during normal operation. Shunt 210 isinserted only during certain system test operations, such as nitrogentests, described below.

Pump/halogen scrubber panel 203 also contains solenoid valves SV9, SV10,and SV11. Valve SV9 allows gas flowing through scrubber HS1 to vent tofitting BH5 under its own pressure. Valve SV11 allows gas flowingthrough scrubber HS1 to be pumped to fitting BH5 via pump P1. Valve SV10allows gas flowing through scrubber HS1 to be pumped using a remotevacuum source connected to fitting BH6. Filter F4 is a filter preventingback flow contamination. Sensor PS2 is a pressure transducer.

II. Test Fixture Description

Both physical embodiments and test procedures in accordance with thepresent invention are now described. The following description firstaddresses check valve and orifice testing. Then, additional test fixturecomponents and testing procedures are described. Throughout theaccompanying figures, solid lines connecting components represent pipesor tubes capable of carrying a gas flow. Embodiments of the invention asdescribed below were constructed with off-the-shelf components and usingindustry standard fabrication methods.

A. General Check Valve Test Description

FIG. 3A is a diagram showing an embodiment of the present invention usedto test check valve opening pressures. The embodiment shown creates asteadily increasing gas pressure ramp against a check valve under test.This pressure ramp is required because a test operator must determinecheck valve opening pressures as exactly as possible, but dataacquisition sampling occurs at a finite rate.

As depicted, gas supply 302 provides a pressurized gas through pressureregulator 304 to needle valve 306. In this embodiment, needle valve 306acts as an orifice and is adjusted to provide a small gas flow toballast tank 308. In other embodiments, any suitable orifice, such as avalve, may be used. Ballast tank 308 is sized, and needle valve 306 isadjusted, to provide a steadily increasing pressure ramp in ballast tank308 at a rate compatible with a desired data sampling rate. Pressuretransducer 310, located upstream of the gas flow to check valve 312under test, monitors increasing ballast tank 308 pressure. Pressuretransducer 314 measures the pressure in the gas flow downstream fromcheck valve 312. In some embodiments, transducers 310 and 314 produce ananalog electric signal corresponding to sensed pressures. In otherembodiments, transducers 310 and 314 may produce other output such asdigital electronic signals or mechanical linkage movements. Inembodiments producing analog electronic signals from transducers 310 and314, the signals are sampled and recorded by a data acquisition systemdescribed in more detail below. Check valve 312 under test is typicallya spring-operated valve designed to allow a gas to flow in a forwarddirection only, as represented by arrow 313. Spring tension is set invalve 312 so that the valve allows gas flow when upstream pressureexceeds the force holding the valve element in place from springtension.

A calculating system, described in more detail below, may determineopening pressure by receiving pressure information from transducers 310and 314 via a data acquisition system, described in more detail below.In some embodiments, the calculating system may be a programmedcomputer. In other embodiments, the calculating system may be adedicated electronic circuit or a mechanical calculating apparatus. Insome embodiments, data acquisition may be performed using interfacecircuits capable of transforming analog transducer signals to digitalform for use by a computer. In other embodiments data acquisitionsystems may produce human-readable outputs such as printouts or graphs.In many embodiments not producing a direct opening pressure indication,a memory system, described in more detail below, exists that is capableof storing information from the data acquisition system for use by thecalculating system. Memory systems may include electronic or magneticstorage, or human-readable printouts. The calculating system maycalculate the valve under test 312's opening pressure by finding thepressure difference between signals from transducers 310 and 314 oncethe downstream pressure starts to rise.

FIG. 3B shows an upstream/downstream differential pressure displayplotting pressure versus time. In some embodiments pressure is displayedin kilopascals (kPa). In other embodiments the test fixture software isconfigured to display and store data in the natively rated pressureunits of selected devices. Manual regulators and check valves, forexample, may be rated in pounds per square inch absolute (psia) or gauge(psig). Time units used are seconds.

Both check and over-pressure valves may exhibit an anomaly in their flowcharacteristics when first opened after being closed for a long time(i.e., they tend to stick closed). This anomaly may be observed as an“overshoot” pressure that exceeds the specification opening pressure setby the internal closing spring. FIG. 3B shows a graphical display of apressure overshoot P_(x), calculated and displayed using pressureinformation from transducers 310 and 314 located upstream and downstreamof a check valve under test 312 as shown in FIG. 3A. The displayedpressure P_(s) represents the valve 312 opening pressure during a steadygas flow at time t₂ after initial opening at time t₁.

Thus, referring again to FIG. 3A, if check valve 312 sticks closed,transducer 310 monitors the upstream pressure rising above the valve 312specification opening pressure. When the valve opens, however,transducers 310 and 314 monitor the upstream/downstream pressuredifferential as the pressure differential drops to the specified minimumpressure. In some embodiments, if the flow below the valve under test312 vents to the outside environment, pressure transducer 314 data maybe omitted and outside pressure information used instead.

B. General Orifice Test Description

FIG. 4 is a diagram showing an embodiment of the present invention usedto test orifice diameter size. Such orifices may be used to restrict gasflows as described above in the gas module (200, FIG. 2) description. Asshown, orifice 410 is the orifice under test.

A gas source 402 supplies a pressurized gas flow via pressure regulator404 and valve 406 to orifice 410. In some embodiments, regulator 404 maybe manually operated. In other embodiments, a remote control device suchas a programmed computer may operate regulator 404. Valve 420 provides ameans to allow gas in line 409 to vent to the outside environment. Beloworifice 410, gas flows between lines 413 and 415 through valve 414.Valve 418 provides a means to allow gas in line 415 to vent to theoutside environment. In the embodiment shown, valves are either fullyopen or fully closed, having no intermediate positions. In someembodiments, valves 406, 414, 418, and 420 may be manually operated. Inother embodiments these valves may be operated using a remotelycontrolled force such as that generated by an electrical signal or gaspressure. Still other embodiments may use a combination of manual andremotely controlled valves.

Pressure transducer 408 measures gas pressure on one side of orifice410, and pressure transducer 412 measures gas pressure on the oppositeside of orifice 410. In some embodiments, transducers 408 and 412 eachproduce an analog electrical signal corresponding to the measuredpressure. In other embodiments, transducers may use other ways ofindicating a sensed pressure, such as a digital electronic signal, amechanical link, or a readable display.

Tank 416 is capable of receiving and holding pressurized gas. Tank 416volume is precisely determined, as is the volume of the additionalplumbing connecting individual components, using measurement orcalculation. Furthermore, typical system gas flow restrictions, such asthose for valves 406 and 414, are conventionally known. Thus, acalculating system (not shown) may calculate tank 416 pressure usingconventional calculations, pressure transducer 412 measurement signals,known system volume and flow restrictions, known environmentalconditions, and known gas laws. Embodiments may include a dataacquisition system, a calculating system, and a memory similar to thatdescribed above under “General Valve Test Description” and described inmore detail below.

A test operator may begin orifice 410 diameter testing by settinginitial conditions. The operator first closes valves 406, 414, 418, and420. The operator then opens valve 418 to set tank 416 internal pressureto the outside environment pressure. Once tank 416 pressure is stable,the operator closes valve 418. The operator then opens valve 414 andmonitors transducers 408 and 412 output signals.

To perform a test, the test operator opens valve 406. A gas flow at apressure regulated by regulator 404 flows through valve 406, throughorifice 410, through valve 414, and begins to fill tank 416. Tank 416fill time will be inversely proportional to orifice 410 averagediameter. Faster tank 416 fill rates result from larger orifice 410average diameters. Transducer 412 senses the increasing tank 416pressure, and a data acquisition system and memory unit record pressureover time. Then using Boyle's and Charles's Laws, and referring tocalibration data using a known orifice diameter as described in detailbelow, a calculating system may determine the actual average diameter oforifice 410 using conventional calculations.

Another embodiment of the test procedure reverses the gas flow directionthrough the orifice under test. Still referring to FIG. 4, a testoperator first closes all valves. The operator then opens valves 406 and414 to allow gas from supply 402 to fill tank 416 until reaching apressure set by regulator 404. The operator then closes valve 406 andmonitors transducer 412. To begin a test, the operator opens valve 420and monitors the transducer 412 pressure output signal as pressurizedgas in tank 416 drains through valve 414, orifice 410, and valve 420.Using information showing tank 416 pressure drain rate system volume andflow restrictions, environment conditions, and gas laws, an operator maycalculate orifice 410's actual average diameter.

The most difficult problem is initial test apparatus calibration becausean orifice of known size must be used to determine a reference pressurerise or fall rate for gas in tank 416. For one embodiment, initialcalibration was performed using a set of very precise custom made laserperforated orifices having diameters in two size ranges. The set in thesmall range included opening diameters from 0.004 inches through 0.023inches in 0.001 inch increments. The set in the large range includedopening diameters from 0.050 inches to 0.075 inches, also in 0.001 inchincrements. The most precise orifices for each particular size incrementwere selected from several nominal production attempts using opticalmicroscope measurements.

At least two selected orifices for each particular size were then testedusing a test fixture embodiment. Test data were gathered and acquisitionerrors smoothed using a standard digital filter algorithm known to thoseskilled in the art. Calibration tables and graphs were then generatedusing this data to give a statistical flow rate representation. Thetables and graphs included positive and negative flow rate limits foruse in test fixture software. Once pressure change rate calibration isaccomplished, however, tests indicate that the method described above issufficiently consistent to detect an improperly sized orifice. Themanual calibration testing and analysis described above indicated thatvariations in the effective diameter of orifice OR4, a 0.013 inchorifice, could be resolved to under 0.0004 inches. Variation in theeffective diameters of 0.063 inch orifices could be resolved toapproximately 0.001 inch.

C. Test Fixture Description

For the embodiment described, tubing used was one-quarter (¼) inchstainless steel with a five (5) microinch (μin.) internal finish.Connections made other than using conventional compression or facesealfittings, such as SWAGELOK or VCR fittings, were typically done usingstandard orbital welding techniques. Such materials and fabricationmethods are standard for constructing semiconductor industry gashandling equipment.

FIGS. 5A and 5B combined show an embodiment of a test fixture 500configured in accordance with the present invention. Components shownwithin dotted line 200 correspond to gas module components to be tested,described above in relation to FIG. 2. Components outside double dottedline 522 comprise test fixture 500. In addition to the gas module 200(FIG. 2) symbols used above, this description uses the followingsymbols:

B: Ballast. A chamber of known volume for holding pressurized gas.

FBH: (Fixture) Bulkhead Fitting

FCV: (Fixture) Check Valve

FF: (Fixture), Filter. Filters are selected to accommodate gas flowrates significantly greater than required for test fixture operation.This “overkill” accommodation ensures that test fixture operation andcalibration are unaffected.

FR: (Fixture) Regulator. In the embodiment shown, regulators supplyinggas pressure from 0-100 psi are TESCOM model 64-2662KRA20 (FR1 and FR3),and the regulator supplying gas pressure from 0-250 psi is TESCOM model64-2663KRA20 (FR2).

FSV: (Fixture) Solenoid Valve

NV: Needle Valve

P: Purifier. In the embodiment shown, the purifier is an AERONEX modelSS-500K-4R.

PR: Pressure Relief Valve

PT: Pressure Transducer. Equivalent to Pressure Sensors in the gasmodule. The embodiment shown may use either SPT model 203 or DATAINSTRUMENTS model SV26.

PV: Pneumatic Valve. Operated by supplying or removing a gas pressure.

VS: Vacuum Sensor. Equivalent to Pressure Sensors/Transducers, but forpressures less than approximately one atmosphere.

Referring to the lower right corner of FIG. 5B, pressurized nitrogen gasis supplied to test fixture 500 through fitting FBH1 from supply 502. A“Dewar” supply, known to those skilled in the art, may be used to avoidfrequent supply bottle changes. Pressure relief valve PR1 providesblow-off protection in case of supplied gas overpressure. Valve PR1 israted at approximately 300 psig. In some embodiments PR1 may be a highvolume, high pressure check valve. In other embodiments PR1 may be arupture valve. Check valve FCV3 prevents back-flow into nitrogen supply502. Valve FCV3 is a high flow ball-type check valve with an openingpressure of approximately one-third (⅓) psi. Purifier P ensures thatvery pure nitrogen is used. In the embodiment shown, purifier P is anAERONEX model SS-500K-4R. Other embodiments may use other purifierunits. Purifier unit specification is not critical as long as ratedpurifier flow rate is significantly greater than the test fixture'srequired flow as described above for test fixture filters. Theembodiment shown uses nitrogen gas with at least 99.999 percent purity.This nitrogen purity level is used during normal laser system operation.Lesser purity nitrogen may leave water or hydrocarbon residue in thedevice under test. After passing through purifier P the nitrogen gas at99.9999999 percent purity enters manifold 504 for distribution withintest fixture 500.

As depicted, nitrogen gas from manifold 504 may be distributedthroughout portions of test fixture 500 at three pressures. RegulatorsFR1, FR2, and FR3 regulate these three pressures. In one embodiment theregulators are set by opening appropriate test fixture valves andmanually adjusting a regulator while observing a display of transducerPT1 and PT2 pressure readings. In the embodiment shown, regulator FR1governs gas flowing to line 506 at 95 pounds-per-square-inch (psi),regulator FR2 governs gas flowing to line 510 at 140 psi,and regulatorFR3 governs gas flowing to line 514 at 50 psi. Pressures of 75-95 psiare required to properly actuate the pneumatic valves. A 140 psipressure is used to create a rising pressure ramp required to test thehigh pressure check valves. The 50 psi pressure simulates the actualoperating pressure of laser system 101. From lines 506, 510, and 514, atest operator may distribute gas within test fixture 500 at the threeregulated pressures by manipulating various valves, as described below.

As shown, regulator FR1 governed nitrogen gas from line 506 is routedthrough filter FF1 and through line 536 to valve manifold 532. FilterFF1 is a simple, off-the-shelf, sintered metal filter that is used toprotect the solenoid valve seats from becoming contaminated withparticulates. The filter specifications are not critical as long as therated flow rate does not restrict test fixture operation. Solenoidvalves FSV1-FSV16 are connected to manifold 532 so that when anindividual solenoid valve receives an electronic activation signal, thevalve opens and allows gas from manifold 532 to flow through aconnecting line (not shown) to a corresponding pneumatically-actuatedtest fixture 500 valve. In the embodiment shown, connections between thesolenoid and pneumatic valves are high-pressure plastic tubing andconventional push-on connectors. For example, solenoid valve FSV1controls a gas flow that may actuate pneumatically-actuated valve PV1,and so on. Solenoid valves FSV1-FSV16 each receive a correspondingactivation signal via an electronic connection (not shown) from a testfixture control unit (not shown), described below. A test operator mayalso direct pressurized gas in line 506 to flow to nitrogen panel 205 byopening valve PV5, and to flow to laser gas panel 201 by then openingvalves PV13 and PV11. Note that up to 140 psi may be applied to fittingBH7 to test valve CV6, which is a 130 psi high pressure relief valve.Check valve FCV1 protects valves FSV1-16 from high gas pressure in line508 in case valve PV5 fails or is inadvertently opened. Pressure sensorPT1 measures gas pressure in line 508 and produces a signal representingthe sensed pressure.

A test operator may direct regulator FR2 governed gas from line 510 togas module 200. Gas from line 510 flows through pneumatically-actuatedvalve PV7, needle valve NV1 and ballast B2 to line 512. Needle valve NV1and ballast B2 provide a configuration for check valve and pressurevalve testing as described above under “General Check Valve TestDescription.” In the embodiment shown, needle valve NV1 is a standardhigh purity stainless steel unit. It is manually adjusted to act inconcert with ballast B2 to produce an increasing pressure ramp rateappropriate for the test time and data acquisition sampling rate. Therange of flow rates controlled by valve NV1 is selected when the actualfixture volumes and data acquisition parameters are known. In someembodiments, ballast B2 is selected to have a volume of 50-100milliliters. Any volume in this range is acceptable. A test operator maydirect pressurized gas from line 512 to nitrogen panel 205 by openingvalve PV13, and to laser gas panel 201 by opening valve PV11. Valve PV3provides a way for gas from line 512 to enter manifold 516. Valves PV1and PV2 provide a way for gas in manifold 516 to be directed to flow tofittings BH1 and BH2, respectively. Sensor PT2 measures the gas pressurein manifold 516 and produces a signal representing the sensed pressure.

A test operator may direct regulator FR3 governed gas to manifold 516 byopening valve PV4. From manifold 516, a test operator may direct a gasflow to laser panel 201 fittings BH1-BH3 by opening valves PV1-PV3,respectively. A test operator may also direct a pressure ramp, createdby needle valve NV1 and ballast B2, to bulkhead fitting BH3 via valvePV11 and through valve PAV3 for the purpose of measuring the pressureresponse of check valve CV4.

Gas from manifold 516 may be dumped to the outside environment byopening valve PV6. Gas then flows through line 520 and filter FF3 tovent V1. Filter FF3 is similar to filter FF1, namely a conventionalsintered metal filter. Filter FF3 prevents contaminants from enteringboth the fixture and the device under test when no positive pressureexists in line 520. Thus a test operator may dump gas from portions oflaser panel 201 by opening valve PV6, and then opening any appropriatecombination of valves PV1-PV3 necessary to drain gas pressure. Inaddition, an operator may dump gas from nitrogen panel 205 by openingvalves PV3, PV11, and PV13. Furthermore, by then opening valve PV5 anoperator may drain gas from valve manifold 532. Gas may be dumped frompump/halogen panel 203 by opening valve PV8.

When a purge gas source is connected to connector V2, the test operatormay direct purge gas throughout laser gas panel 201 and pump/halogenscrubber panel 203. This act allows flushing any contaminants andevaporating any moisture from the high purity gas manifolds of thedevice under test. Manifold flushing is accomplished by sequentiallyoperating all valves in laser gas panel 201, the valves and pump inpump/halogen scrubber panel 203, and valves PV1-3, PV9, and PV10.

Referring to the upper left corner of FIG. 5A, a 2.5 liter chamber 526is shown. Chamber 526 is capable of containing pressurized gas and isused during orifice testing as described above under “General OrificeTest Description.” Sensor PT3 measures gas pressure in chamber 526 andproduces a signal corresponding to measured pressure. Chamber 526 isconnected to manifold 528 via valve PV9. Manifold 528 may then beconnected to laser panel 201 fitting BH4. Chamber 526 is also connectedto line 520 via valve PV10. This connection provides a way for a testoperator to dump gas from chamber 526 through filter FF3 and vent V3 tothe outside environment.

Also shown is leak detector 524, connected to manifold 528 via valvePV14. Leak detector 524 comprises an external helium detector and avacuum pump, as known to those skilled in the art of vacuum technology,and is used during gas module 200 leak testing, described below.

Referring to the upper right corner of FIG. 5B, ballast B1 is shown.Ballast B1 is selected to have a volume of 50-100 ml, and is similar toballast B2. Sensor PT4 measures ballast B1 gas pressure and produces asignal representing the measured pressure. Ballast B1 is connected tonitrogen panel 205 fitting BH10 via line 530 and shutter mechanism 212,described above. Note that the LEGRIS fitting inherently has some gasleakage around the push-in engagement mechanism for the plastic tubingconnecting the LEGRIS with laser shutter 212. The gas volume normallyleaked is trivial compared with the gas flow volume to laser shutter212. A test operator may dump gas from ballast B1 and line 530 byopening valve PV12 and allowing gas to flow through vent V4 to theoutside environment. Rotameter ROTA1 measures gas flow as it drainsthrough vent V4. A test operator may observe rotameter ROTA1 gas flow tomake final adjustment to gas flow through orifice OR6 to beapproximately correct for laser shutter operation when a gas module (gasmodule 200, FIG. 2, for example) is initially installed in a laser(laser system 101, FIG. 1, for example).

Also shown is pressure sensor PTX. Sensor PTX measures barometricpressure of the outside environment and produces a signal representingthe measured pressure. The test operator may use this signal toprecalibrate all other sensor/transducer readings during gas module 200test procedures.

Finally, referring to the lower right corner of FIG. 5A, manifold 513 isshown connected to gas module 200 fitting BH6. Gas in manifold 513 mayvent to the outside environment through check valve FCV2, which in thisembodiment is a high flow, ball-type check valve with an openingpressure rating of approximately one-third (⅓) psi, through filter FF2which is an off-the-shelf sintered metal filter, similar to filter FF1,having a flow rating sufficient so as to cause no flow restriction, andthrough vent V5. Vacuum sensor VS1 measures gas pressures in manifold513 that are below approximately one (1) atmosphere and produces asignal representing the measured pressure. In the embodiment shown,sensor VS1 is an OMEGA model PX542. A test operator may protect sensorVS1 from damaging gas overpressure by closing valve PV16.

FIG. 6 is a block diagram showing an embodiment of the invention. Testfixture 602 is shown connected so that both pressurized gas 614 andelectrical control and data signals 616 may travel between fixturehardware 604 and laser gas module 612 under test. For example, gas 614may comprise gas flowing between test fixture hardware 500 and gasmodule 200 though fittings BH1-7 and BH10 as shown in FIGS. 5A and 5B.Signals 616, for example, may comprise pressure signals from sensorsPS1-3 and actuating signals supplied to valves SV1-11 and pump P1 alsoshown in FIGS. 5A and 5B. Signals 616 may also comprise calibrationsignals for sensors PS1-3 and control signals for regulators FR1-3.

Fixture hardware 604 may include both pressurized gas supply apparatus,such as that described above in relation to FIGS. 5A and 5B, andelectronic circuits that provide a data acquisition interface betweengas module 612 and computer 608. In one embodiment, data acquisitioninterface circuitry includes conventional interface circuitsmanufactured by NATIONAL INSTRUMENTS, Inc. In the embodiment shown, allcontrol and measurement signals sent between test fixture 602 and gasmodule 612 are routed through these installed circuits. Fixture hardware604 is chosen to be compatible with test sequencing software describedbelow, and to provide data transfer rates appropriate for tests to beperformed. Conventional electronics, such as opto-isolator relays todrive solenoid valves, are used for the interface between computer 608and plumbing components in both test fixture 602 and gas module 612. Inother embodiments, other interface circuit configurations may be used. Amemory 610 for storing information is shown connected to computer 608.Information stored in memory 610 may include one or more necessarycomputer programs and results of test procedures conducted in accordancewith this invention. As depicted, memory 610 may be any electronic ormagnetic data storage device capable of being connected to an electroniccomputing network. In other embodiments memory 610 may include printoutsor written records of test results.

In the embodiment shown, test fixture 602 hosts all test program, datamanagement, user interface, and network interconnection needs. In oneembodiment computer 608 is an IBM-compatible personal computerconfigured with MICROSOFT WINDOWS NT and MICROSOFT NETWORK. In otherembodiments computer 608 may be configured with any conventionaloperating system and/or networking program. Operator interface 606 isconnected to computer 608 so that an operator may issue commands to, andreceive information from, computer 608. Interface 606 may include avisual display, a keyboard, and/or a mouse or other pointing device.

In one embodiment computer 608 is configured to operate with programswritten in LABVIEW, a programming language provided by NATIONALINSTRUMENTS, Inc., to provide a graphical operator interface display oninterface 606. A particular benefit of this control embodiment is thedeveloped software's graphical interface. LABVIEW allows graphicaldisplay and control of gas plumbing components in both gas module 612under test and test fixture 602. Thus, test fixture 602 may be adaptedto test a particular laser gas module 612.

The software is configured to automatically execute complex testsequences with minimal test operator intervention. Tasks may includesetting gas regulator pressures (via digitally controlled regulatordevices), calibrating and adjusting sensors and transducers, actuatingvalves in precise sequences, acquiring data, and recording all testconditions and results.

Individual tests may consist of an action sequence to carry outembodiments of the general test methods described above as well as othertests described below. The software may be configured to execute aparticular sequence comprising a single test, a group of tests, and arepetition of any single test or group of tests.

In addition, in this embodiment the test software provides indicationsfor manual operation of all controlled devices (valves, regulators,etc.) and direct reading of all data signals. All device control anddata signals may be handled through a computer-controlled user interface606. Thus a test operator may be required to abandon user interface 606only to operate manual valves and regulators or to read mechanicalindicators.

The test fixture user interface 606 is designed to graphically representthe actual schematic design of the gas module, the test fixture, and theinterconnections between the gas module and the test fixture. Thisrepresentation includes all tubing, valves, regulators, sensors andtransducers, orifices, check and overpressure valves, externalconnectors, chambers, needle valves, filters, pumps, and all other fluidprocessing devices and connections that are part of the gas module orthe fixture.

All data source devices that produce data signals (i.e., devices otherthan strictly mechanical gauges) may be represented on the computerinterface 606 screen. For example, in one embodiment the fixturecontinuously displays real-time data values from pressure transducers.Data may be updated and displayed both during and apart from testoperations. Thus, monitoring device calibration, such as pressure sensorcalibration, is facilitated during test fixture idle time.

User interface 606 may continuously display a data graph. The displaymay also include an associated menu containing a list of all of datasources shown on the graphical device schematics. The test operator mayselect any one or combination of listed data sources and their real-timevalues will be continuously added to the running, time-based graph. Thedata graph may be started and stopped via a virtual button on theinterface 606 screen to permit data gathering and graphing during achosen period. An automatic test sequence program statement may alsostart and stop the data graphing operation.

The data graph display may further incorporate a system of cursors anddata point readout aids which assist data analysis when the graphingfunction is stopped. The data graph display may incorporate provisionsfor saving the collected and displayed data to a memory 610. Forexample, in one embodiment, saving data creates a text filerepresentation of all floating point data, with each data sourcerepresented in a separate column. A time interval column isautomatically generated parallel to the data points, and the file has aprepended header that identifies the reference designator of a devicewhich generated each column of data points, along with test time andinitial condition information.

All user interface-controllable device states may be displayed usingcolor and shape changes on the displayed interface 606 schematicrepresentation. This device state display provides a clear and instantvisual representation of open fluid paths. In one embodiment, thefixture continuously updates and displays all software-controlled devicestates on user interface 606 regardless of manual or automatic testsequence mode operation.

During automatic test sequences, computer 608 may collect all test dataand saves them in memory 610. Data stored may include operatoridentification, test fixture identification, test softwareidentification and version information, gas module 612 part and revisionnumbers, gas module 612 serial number, initial ambient conditions, teststart/stop time stamps, pass/fail data by sequence ID or parameter, andanalog data for critical measurement parameters. Memory 610 may be ahuman readable text-based dump, or may be a data base.

D. Test Description Preparation for Gas Module Testing

Referring again to FIGS. 5A and 5B, testing may begin by connecting testfixture 500 to gas module 200 and laser chamber 208 at all bulkheadfittings (BHs), and electrical connections (not shown) for sending andreceiving control and data signals, appropriate for the test(s) to beconducted. The connections are conventional and allow gas and bothsensor and control signals to pass among test fixture 500, gas module200, and laser components such as shutter 212. Fixture BH6 may beinitially capped and sealed in a conventional manner, may be opened, ormay have additional test equipment attached if required as necessary asdescribed below. In some test sequence embodiments, shunt 210 ismanually inserted.

For initial set-up, an operator may close all solenoid valves, manuallyclose valves MV1-4 in nitrogen panel 205, and manually open valve SOl inlaser gas panel 201. An operator may then set regulators FR1, FR2, andFR3 to govern gas pressures as desired (95, 140, and 50 psi,respectively, for example). An operator may manually close orifice OR6.And, an operator may set a needle valve NV1 opening so as to adjust gasentering ballast B2 to produce a desired fill rate.

Nitrogen panel 205 components are typically tested first becausenitrogen gas drives other gas module components. After a test operatortests nitrogen panel 205 components he may test the remaining gas module200 components.

Rather than describe a complete test sequence, which may be varied as atest operator requires, the remaining discussion is organized topicallyby test function. Those skilled in the art will understand that specifictest sequences described represent one or more embodiments of theinvention. Many test sequence variations exist in accordance with thepresent invention for both operational and development testing of a gasmodule.

Valve Logic Test

A test operator may test valve logic to ensure that the correct pressureactuated valve opens when a control signal is applied to itscorresponding solenoid valve. The operator may manipulate test fixture500 valves so as to apply pressurized gas to a closed pneumatic-actuatedvalve in gas module 200. Then the operator supplies an opening signal tothe corresponding solenoid valve and monitors an appropriate pressuresensor for a pressure increase downstream of the valve under test.

For example, an operator may test laser gas panel 201 valve PAV1 byopening valves PV4 and PV1 and applying an activation signal to solenoidvalve SV1. If pressure rises on sensor PS1, valve PAV1 has opened. Otherpneumatic valves may be similarly tested.

An operator may also test proper valve activation by monitoring for apressure drop after sending an opening signal to a valve under test. Asshown in this embodiment, an operator may test laser gas panel 201solenoid valves SV9, SV10, and SV11 by pressurizing manifold 216 andmonitoring sensor PS2. When valve SV9, SV10, or SV11 receives an openingsignal, sensor PS2 senses the manifold 216 gas pressure drop as gasflows out through fitting BH5 or BH6 as applicable.

Check and Relief Valve Tests

Using the embodiment shown, a test operator may conduct tests of checkand relief valve opening pressures in a manner similar to that describedabove under “General Check Valve Test Description.” Needle valve NV1 andballast B2 function in a way similar to that described for valve 306 andballast 308 in the description accompanying FIG. 3A, above. In theembodiment shown in FIGS. 5A and 5B, ballast B2 is a known volumecanister in the range of 50-100 milliliters. Valve NV1 is adjusted toprovide a small gas flow causing a desired rising gas pressure ramp inballast B2. In one test sequence embodiment, ramp rates used wereapproximately 3-4 seconds. This time was ample for sampling and to allowtransducer settling (typically on the order of 10 milliseconds for thedevices used herein).

To test valve CV3, for example, a test operator may begin by opening allvalves downstream of valves PV13 and PV7 and removing gas pressure frommanifold 202 and fittings BH1, BH2, and BH3, and then closing allvalves. The operator then opens valve PV3 to allow sensor PT2 to monitorballast B2 gas pressure upstream of valve CV3 under test, and opensvalve PAV3 to allow sensor PS1 to monitor manifold 202 gas pressurebelow valve CV3. The operator opens valve PV11 to route gas from ballastB2 to valve CV3.

To conduct the test, the tester opens valve PV7. A gas pressure rampbuilds in ballast B2, measured by transducer PT2. Sensor PS1 indicateswhen valve CV3 opens. The peak reading from PT2 will indicate the actualmaximum opening pressure of CV3. The test operator may then close PV11and open PV6 to vent positive pressure in manifold 516 while manifold202 remains pressurized from the previous actions. The test operator maythen verify that CV3 has once again closed, and may measure CV3'sleakage by monitoring PS1's output signal. Referring to FIG. 6, computer608 receives signals from transducers PT2 and PS1 (FIG. 5A) throughfixture hardware 604, determines opening pressure against time withdifference calculations, stores the result in memory 610, and produces adisplay on interface 606.

Referring again to FIGS. 5A and 5B, check valves CV1 and CV2 may betested in a way similar to that used for valve CV3 as described above.To test valves CV1 and CV2, however, the tester opens valves PV1 and PV2as required to route gas to the check valve under test, and opens valvesPAV1 and PAV2 to allow sensor PS1 to measure pressure below the checkvalve under test.

Check valve CV4 may be similarly tested. Check valve CV4, having asignificant specified opening pressure as described above, is morelikely to stick. Valve PV4 is closed to remove normal operating inputpressure. Valve SV10 is opened to remove back pressure from valve CV4(fitting BH6 is uncapped). Valves PV11 and PAV3 are opened, and thenvalve PV7 is opened to apply a high pressure ramp to valve CV4 throughballast B2. Sensor PS1 monitors the increasing pressure ramp and sensorPS2 monitors pressure below valve CV4. As described above, the resultingpressure differential indicates valve CV4 opening pressure.

Valves CV5 and CV6 are tested similarly, except the tester monitors onlyupstream pressure because the valves vent to the outside environment.Outside pressure may be supplied by transducer PTX or other indicator.When the tester opens valve PV8, for example, valve CV5 vents throughfilter FF3. Valve CV6 vents through fitting V1. Shunt 210 is inserted.Gas is routed to valve CV5 by opening valves PV11, PAV3, and PAV4. Gasis routed to valve CV6 using valve PV13. During the test, sensor PS2measures valve CV5 upstream pressure and transducer PT1 measures valveCV6 upstream pressure.

Valve CV7 may be tested by closing needle valve OR6, pressurizingmanifold 214, opening solenoid valve SV7, and observing a slow pressurerise indicated by a transducer PT4 output signal. A slow pressure riseis normally observed because needle valve OR6 may not close to a fullseal.

Leak Testing

A typical gas module has an extremely small leak tolerance. Stillreferring to FIGS. 5A and 5B, a test operator may use the embodimentshown to conduct a conventional helium leak detection test of laser gaspanel 201. An operator may isolate laser gas panel 201 by closing valvesor capping fittings BH1-BH3, BH5, and BH6 as appropriate, and by closingvalve PV9. The operator may then open all laser gas panel 201 internalvalves. The test operator then activates leak detector 524, whichcreates a vacuum pressure, and opens valve PV14. The gas module pressuretransducers are selected from standard components to accommodate apressure range including zero psia. The test operator may then manuallyapply a small helium stream to all gas fittings and plumbing using ahand-held nozzle. If a leak exists, a vacuum pump in leak detector 524draws the applied helium through the leak opening. Leak detector 524then detects the helium and produces an output signal received bycomputer 608 via fixture hardware 604 (FIG. 6). Note that although aleak test of a nitrogen panel may be performed, solenoid valvestypically have some leakage and the expense of any normally leakednitrogen gas is trivial. Test procedures concentrate on componentsaccommodating gas comprising fluorine.

In addition to using a conventional helium leak test, a test operatormay measure leakage using a volume transfer method. The approximate gasmodule and test fixture plumbing volumes may be measured or calculated.The test operator then pressurizes the appropriate plumbing and monitorsan appropriate pressure sensor. Any pressure rise or decrease at aspecified location indicates a leak, and the leak rate may be calculatedusing known gas laws.

For example, valves PAV1-PAV3 may be leak tested by applying gaspressure to their inputs through fittings BH1-BH3, respectively, andusing sensor PS1 to monitor for any output pressure rise. A lack ofpressure rise in manifold 202 shows that no “forward” pressure leakexists for the valve under test. Forward pressure as used here meanspressure applied as the result of gas flowing in the direction normallyused during laser operation. Then, manifold 202 may be pressurized,valves PAV1-6 are closed, and the test operator monitors sensor PS1 forany pressure drop. A pressure drop indicates that one of the valves has“reverse” pressure leak. Reverse pressure as used here means pressureapplied as the result of gas flowing in the direction opposite thedirection normally used during laser operation. An operator may leaktest remaining gas module 200 and test fixture 500 components using asimilar volumetric approach.

Check valves may be “reverse” leak tested by pressurizing the linedownstream of the valve under test, removing the supply upstream of thevalve under test, and monitoring for pressure decrease. For example,valves CV1, CV2, and CV3 may be checked by pressurizing manifold 202 byopening valves PV1-PV3, and then opening and subsequently closing valvePV4. The operator then opens valve PV6 to provide a gas route throughvent V3. If sensor PS1 output detects any leak, the operator may isolatethe leaking check valve by repressurizing and manipulating valves PV1,PV2, and PV3 in turn.

Orifice Testing

The operator may carry out orifice testing using an embodiment of theinvention shown in FIGS. 5A and 5B, as described above under “GeneralOrifice Test Description.” As shown, a 2.5 liter chamber 526 is used asa known volume tank (416, FIG. 4) because an actual laser chamber 208has a much greater volume. Using the smaller chamber 526 shortens filltime and saves expensive gas.

To test orifice OR3 for example, a test operator opens valve PV10 andallows chamber 506 pressure to stabilize at outside environmentpressure. Then the operator stabilizes manifold 202 at chamber 526pressure by opening valve PV9 and valve PAV5. When chamber 526 andmanifold 202 pressures stabilize, the operator closes valve PV10 andapplies a desired gas pressure to fitting BH3 by manipulatingappropriate test fixture 500 valves. The test begins when operator opensvalve PAV3. Orifice OR3 controls chamber 526 fill rate as monitored bysensor PT3. Using procedures as described above in relation to FIG. 4, acomputer 608 (FIG. 6) may calculate orifice OR3 average diameter byreceiving data signals used to show chamber 526's fill rate over time. Atest operator may test orifices OR1, OR2, and OR4 using this method bymanipulating the necessary gas module 200 valves.

A test operator may test orifice OR5 using another embodiment of themethod for orifice testing as described above under “General OrificeTest Description.” The test operator may pressurize chamber 526 and thenclose valve PV9, thereby holding a high gas pressure in chamber 526. Thetest operator then opens valve SO1 and monitors transducer PT3 pressureoutput signal. To begin the test, the test operator opens valves SV10and PV9 so that chamber 526 pressure drains to the outside environmentthrough orifice OR5. Once again a computer 608 (FIG. 6) may calculateorifice OR5 average diameter using the pressure decrease rate and knownsystem restrictions, and referencing calibration data as described indetail above.

Opening chamber 526 to the atmosphere may introduce water vapor to thesystem. Test embodiments as described herein, however, were designed tobe performed in a clean room environment with controlled humidity. Thehot purge gas inlet V2 at PV15 allows the device under test to be driedout with heated nitrogen before the device under test is sealed and sentto WIP stores or to an operating laser system.

Nitrogen panel 205's adjustable needle valve OR6 average openingdiameter may be tested using the same method as for testing orifice OR5.A test operator may stabilize ballast B1 gas pressure by opening valvePV12. The test operator then directs pressurized gas to fill ballast B1by pressurizing manifold 214 and opening valve SV7. Gas then begins tofill ballast B1 by flowing through needle valve OR6. Sensor PT4 monitorsballast B1 pressure increase and thus valve OR6 average opening diametermay be determined. A test operator may also use this test sequence valvesetting to provide leak information and an initial setting for needlevalve OR6.

For a laser system 101 (FIG. 1) operation a laser system operator mustset an average orifice diameter for needle valve OR6 to provide arequired gas flow amount to properly actuate laser system shutter 212.In the embodiment shown, an operator may do this by pressurizingmanifold 214, opening valves SV7 and PV12, and manually adjusting valveOR6 to obtain the desired flow as indicated by rotameter ROTA1.

Pump Testing

In the embodiment shown, pressure transducers in test fixture 500 andgas module 200 are silicon strain-gauge positive pressure transducersselected to withstand low pressures caused by pump P1. Their calibrationdoes not provide adequate resolution at very low pressures. Sensor VS1,however, is a low-pressure transducer that is appropriate for measuringthe vacuum pump pressures developed by pump P1.

For pump P1 testing, valves PV8-10, PV16, PAV4-5, and SV9-11 are openedto allow manifold 216 and chamber to attain ambient pressure. Then, allvalves except SV10 and PV16 are closed. In one embodiment, software isconfigured to protect sensor VS1 by preventing valve PV16 from openingif a sensor PS2 output signal indicates a pressure significantly aboveambient pressure. Valves SV9 and SV11 are opened to ensure that pump P1does not start against a pressure head.

To begin the test, valves PV8-9, PAV4-5, and SV11 are opened and pump P1is started. Valve PV8 provides a pump outflow path via line 518. Pump P1operation is acceptable if a sensor VS1 output signal has a specifiedmaximum pressure reading after a specified run time.

While the present invention has been described in terms of specificembodiments, those skilled in the art will appreciate that manymodifications and variations exist that fall within the spirit and scopeof the present invention.

We claim:
 1. A gas module orifice test fixture comprising: a tank having an inlet port, said tank being capable of holding a quantity of pressurized gas; a pressure regulated gas source connected using a gas line to said inlet port; an orifice under test positioned in said gas line between said gas source and said tank such that gas flowing in said gas line must pass through said orifice under test; and a pressure sensor positioned to sense gas pressure in said gas line on a first side of said orifice under test, said pressure sensor producing a first pressure signal.
 2. The apparatus of claim 1 further comprising a calculator electrically coupled to receive said first pressure signal, wherein said calculator is adapted to use said first pressure signal to calculate said orifice under test's average diameter.
 3. The apparatus of claim 2 wherein said calculator comprises a visual display of elements of said test fixture, and allows control of selected said components of said test fixture with a pointing device.
 4. The apparatus of claim 1 wherein said first pressure signal comprises a digitally sampled signal of a predetermined sampling rate.
 5. The apparatus of claim 1 further comprising: a second pressure sensor connected to measure gas pressure in said gas line on a side of said orifice under test opposite said first side, said second pressure sensor producing a second pressure signal; and a calculator electrically coupled to receive said first and said second pressure signals; wherein said calculator uses said first and said second pressure signals to calculate said orifice under test's average diameter.
 6. A method of determining gas flow restricting orifice average diameter comprising: directing a gas flow through said gas flow restricting orifice so as to pressurize a container; producing a data signal by measuring increasing gas pressure in said container as said gas flow enters said chamber; calculating an average diameter of said gas flow restricting orifice by using said data signal.
 7. The method of claim 6 wherein said calculating comprises comparing increasing pressure information derived from said data signal to increasing pressure information when said container is pressurized through a second gas flow restricting orifice of known average diameter.
 8. The method of claim 7 further comprising: providing a visual display of elements of a test fixture; and controlling operation of selected of said elements of said test fixture by using a pointing device on said visual display. 